Commercial space pioneer Elon Musk has already accomplished something that previously only three nations had done before: launched and returned a spacecraft safely from orbit. But the rocket builder isn't stopping there, and TV's Jon Stewart wants to know why.

SpaceX is scheduled to launch its robotic Dragon spacecraft to the orbiting outpost on April 30. The mission is designed to test the capsule's ability to haul cargo to the complex. If successful, Dragon will be the first privately built spacecraft to rendezvous and dock with the space station.

"The four entities that have done that are the United States, China, the Soviet Union and Elon Musk," Stewart said as he welcomed the entrepreneur onto Comedy Central's popular talk show. [ Gallery: Dragon, SpaceX's Private Spacecraft ]

"Yes, that's right," Musk said. "I had some help, but yeah."

Musk, who founded SpaceX in 2002, is also the CEO of Tesla Motors and co-founder of the online payment system PayPal. He told the TV comedian that his ambitions took root in college, when he identified three primary areas of interest: the Internet, sustainable energy and space exploration.

Science editor Alan Boyle's blog: "Astronaut Abby" is at the controls of a social-media machine that is launching the 15-year-old from Minnesota to Kazakhstan this month for the liftoff of the International Space Station's next crew.

SpaceX eventually plans to use a version of the Dragon capsule to carry astronauts and other paying customers to low-Earth orbit. As the company grows and sets even loftier goals, the spaceflight firm could find themselves competing not only with other private enterprises, but other nations as well.

"It is a strange place to be," Musk said, acknowledging the role of his company in the future of commercial spaceflight. "The head of the Russian space program is coming to visit soon."

You can follow Space.com staff writer Denise Chow on Twitter @denisechow. Follow Space.com for the latest in space science and exploration news on Twitter @Spacedotcom and on Facebook.